Medullary and cortical thick ascending limb: similarities and differences

The thick ascending limb of the loop of Henle (TAL) is the first segment of the distal nephron, extending through the whole outer medulla and cortex, two regions with different composition of the peritubular environment. The TAL plays a critical role in the control of NaCl, water, acid, and divalent cation homeostasis, as illustrated by the consequences of the various monogenic diseases that affect the TAL. It delivers tubular fluid to the distal convoluted tubule and thereby affects the function of the downstream tubular segments. The TAL is commonly considered as a whole. However, many structural and functional differences exist between its medullary and cortical parts. The present review summarizes the available data regarding the similarities and differences between the medullary and cortical parts of the TAL. Both subsegments reabsorb NaCl and have high Na+-K+-ATPase activity and negligible water permeability; however, they express distinct isoforms of the Na+-K+-2Cl− cotransporter at the apical membrane. Ammonia and bicarbonate are mostly reabsorbed in the medullary TAL, whereas Ca2+ and Mg2+ are mostly reabsorbed in the cortical TAL. The peptidic hormone receptors controlling transport in the TAL are not homogeneously expressed along the cortical and medullary TAL. Besides this axial heterogeneity, structural and functional differences are also apparent between species, which underscores the link between properties and role of the TAL under various environments.

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Regulation of sodium transporters in the thick ascending limb of rat kidney: response to angiotensin II

AJP Renal Physiology ◽

10.1152/ajprenal.00307.2002 ◽

2003 ◽

Vol 285 (1) ◽

pp. F152-F165 ◽

Cited By ~ 87

Author(s):

Tae-Hwan Kwon ◽

Jakob Nielsen ◽

Young-Hee Kim ◽

Mark A. Knepper ◽

Jørgen Frøkiær ◽

...

Keyword(s):

Proximal Tubule ◽

Brush Border ◽

Rat Kidney ◽

Thick Ascending Limb ◽

Ang Ii ◽

Outer Medulla ◽

Protein Protein Interaction ◽

Sodium Transporters ◽

Outer Strip

The effect of ANG II treatment of rats for 7 days was examined with respect to the abundance and subcellular localization of key thick ascending limb (TAL) Na+ transporters. Rats were on a fixed intake of Na+ and water and treated with 0, 12.5, 25, 50 (ANG II-50), 100 (ANG II-100), and 200 (ANG II-200) ng·min-1·kg-1 ANG II (sc). Semiquantitative immunoblotting revealed that Na+/H+ exchanger 3 (NHE3) abundance in the inner stripe of the outer medulla (ISOM) of ANG II-treated rats was significantly increased: 179 ± 28 (ANG II-50, n = 5), 166 ± 23 (ANG II-100, n = 7), and 167 ± 19% (ANG II-200, n = 4) of control levels ( n = 6, P < 0.05), whereas lower doses of ANG II were ineffective. The abundance of the bumetanide-sensitive Na+-K+-2Cl- cotransporter (BSC-1) in the ISOM was also increased to 187 ± 28 (ANG II-50), 162 ± 23 (ANG II-100), and 166 ± 19% (ANG II-200) of control levels ( P < 0.05), but there were no changes in the abundance of Na+-K+-ATPase and the electroneutral Na+-HCO3 cotransporter NBCn1. Immunocytochemistry confirmed the increase in NHE3 and BSC-1 labeling in medullary TAL (mTAL). In the cortex and the outer strip of the outer medulla, NHE3 abundance was unchanged, whereas immunocytochemistry revealed markedly increased NHE3 labeling of the proximal tubule brush border, suggesting subcellular redistribution of NHE3 or differential protein-protein interaction. Despite this, ANG II-treated rats (50 ng·min-1·kg-1 for 5 days, n = 6) had a higher urinary pH compared with controls. NH4Cl loading completely blocked all effects of ANG II infusion on NHE3 and BSC-1, suggesting a potential role of pH as a mediator of these effects. In conclusion, increased abundance of NHE3 and BSC-1 in mTAL cells as well as increased NHE3 in the proximal tubule brush border may contribute to enhanced renal Na+ and HCO3 reabsorption in response to ANG II.

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Pharmacological Evidence For A Critical Role Of Apical Membrane Two-pore Potassium (K2P) Channels In Regulating Sodium Absorption And Chloride Secretion In Normal Human Bronchial Epithelial Cells

10.1164/ajrccm-conference.2010.181.1_meetingabstracts.a6456 ◽

2010 ◽

Author(s):

Amy N. Savitski ◽

James L. Kreindler

Keyword(s):

Apical Membrane ◽

Critical Role ◽

Chloride Secretion ◽

Sodium Absorption ◽

Normal Human Bronchial Epithelial ◽

Human Bronchial Epithelial Cells ◽

Bronchial Epithelial ◽

K2p Channels ◽

Normal Human

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cAMP increases surface expression of NKCC2 in rat thick ascending limbs: role of VAMP

AJP Renal Physiology ◽

10.1152/ajprenal.00248.2005 ◽

2006 ◽

Vol 290 (3) ◽

pp. F608-F616 ◽

Cited By ~ 81

Author(s):

Pablo A. Ortiz

Keyword(s):

Confocal Microscopy ◽

Membrane Protein ◽

Tetanus Toxin ◽

Apical Membrane ◽

Surface Expression ◽

Thick Ascending Limb ◽

Dibutyryl Camp ◽

Nacl Absorption ◽

Stimulation Of

NaCl absorption by the thick ascending limb of Henle’s loop (TAL) is mediated by the apical Na-K-2Cl cotransporter NKCC2. cAMP increases NaCl absorption in the TAL by stimulating NKCC2. In oocytes, cAMP increases NKCC2 activity by regulating its trafficking. However, the mechanism by which cAMP stimulates NKCC2 in TALs is not clear. We hypothesized that cAMP increases surface expression of NKCC2 and NaCl absorption in TALs and that vesicle-associated membrane protein (VAMP) is involved in this mechanism. We used surface biotinylation of rat medullary TALs (mTAL) to examine surface and total NKCC2 levels. When mTAL suspensions were treated with dibutyryl cAMP (db-cAMP) or forskolin plus IBMX for 20 min, surface NKCC2 expression increased by 126 ± 23 and 92 ± 17% above basal, respectively ( P < 0.03). No changes in total NKCC2 expression were observed, suggesting that cAMP increased translocation of NKCC2. We studied the role of VAMP in NKCC2 translocation and found that incubating mTALs with tetanus toxin (30 nM), which inhibits vesicle trafficking by inactivating VAMP-2 and -3, completely blocked the stimulatory effect of db-cAMP on surface NKCC2 expression (tetanus toxin = 100% vs. tetanus toxin + db-cAMP = 102 ± 21% of control; not significant). We studied VAMP-2 and -3 expression and localization in isolated perfused TALs by confocal microscopy and found that both of them were located in the subapical space of the TAL. Finally, in isolated perfused mTALs, db-cAMP increased net Cl absorption by 95.0 ± 34.8% ( P < 0.03), and pretreatment of TALs with tetanus toxin blocked the stimulation of Cl absorption (from 110.9 ± 15.9 to 109.7 ± 15.6 pmol·min−1·mm−1; not significant). We concluded that cAMP increases NKCC2 surface expression by a mechanism involving VAMP and that NKCC2 trafficking to the apical membrane is involved in the stimulation of TAL NaCl absorption by cAMP.

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mTOR-activating mutations in RRAGD cause kidney tubulopathy and cardiomyopathy (KICA) syndrome

10.1101/2021.03.11.434334 ◽

2021 ◽

Author(s):

Karl P. Schlingmann ◽

François Jouret ◽

Kuang Shen ◽

Anukrati Nigam ◽

Francisco J. Arjona ◽

...

Keyword(s):

Cardiac Function ◽

Dilated Cardiomyopathy ◽

Critical Role ◽

Genetic Diagnosis ◽

Mtor Signaling ◽

Thick Ascending Limb ◽

Salt Wasting ◽

Constitutive Activation

ABSTRACTBackgroundOver the last decaces, advances in genetic techniques have resulted in the identification of rare hereditary disorders of renal magnesium and salt handling. Nevertheless, ±20% of all tubulopathy patients remain without genetic diagnosis. Here, we explore a large multicentric patient cohort with a novel inherited salt-losing tubulopathy, hypomagnesemia and dilated cardiomyopathy (DCM).MethodsWhole exome and genome sequencings were performed with various subsequent functional analyses of identified RRAGD variants in vitro.ResultsIn 8 children from unrelated families with a tubulopathy characterized by hypomagnesemia, hypokalemia, salt-wasting, and nephrocalcinosis, we identified heterozygous missense variants in RRAGD that mostly occurred de novo. Six of these patients additionally suffered from DCM requiring heart transplantation in 3 of them. An additional dominant variant in RRAGD was simultaneously identified in eight members of a large family with a similar renal phenotype. RRAGD encodes GTPase RagD mediating amino acid signaling to the mechanistic target of rapamycin complex 1 (mTORC1). RagD expression along the mammalian nephron include the thick ascending limb and the distal convoluted tubule. The identified RRAGD variants were shown to induce a constitutive activation of mTOR signaling in vitro,ConclusionsOur findings establish a novel disease phenotype combining kidney tubulopathy and cardiomyopathy (KICA) caused by an activation of mTOR signaling suggesting a critical role of Rag GTPase D for renal electrolyte handling and cardiac function.SIGNIFICANCE STATEMENTHere, we report on heterozygous variants in RRAGD in patients with profound hypomagnesemia, renal salt wasting, nephrocalcinosis, and dilated cardiomyopathy. The identified RagD variants induce a constitutive activation of mTOR signaling in vitro. These findings not only establish a novel monogenic disorder of the kidney tubule, but demonstrate the essential role of mTOR signaling for distal tubular electrolyte handling and cardiac function.

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Regulation of Potassium Channel Kir 1.1 (ROMK) Abundance in the Thick Ascending Limb of Henle's Loop

Journal of the American Society of Nephrology ◽

10.1681/asn.v12110 ◽

2001 ◽

Vol 12 (1) ◽

pp. 10-18

Author(s):

CAROLYN A. ECELBARGER ◽

GHEUN-HO KIM ◽

MARK A. KNEPPER ◽

JIE LIU ◽

MARGARET TATE ◽

...

Keyword(s):

Potassium Channel ◽

Apical Membrane ◽

Rat Kidney ◽

Thick Ascending Limb ◽

Outer Medulla ◽

Cos Cells ◽

Selective Agonist ◽

V2 Receptor ◽

Counter Current

Abstract. The renal outer medullary potassium channel (ROMK) of the thick ascending limb (TAL) is a critical component of the counter-current multiplication mechanism. In this study, two new antibodies raised to ROMK were used to investigate changes in the renal abundance of ROMK with treatments known to strongly promote TAL function. These antibodies specifically recognized protein of the predicted size of 45 kD in immunoblots of rat kidney or COS cells transfected with ROMK cDNA. Infusion of 1-deamino-(8-D-arginine)-vasopressin (dDAVP), a vasopressin V2 receptor-selective agonist, for 7 d into Brattleboro rats resulted in dramatic increases in apical membrane labeling of ROMK in the TAL of dDAVP-treated rats, as assessed by immunocytochemical analyses. Using immunoblotting, a more than threefold increase in immunoreactive ROMK levels was observed in the outer medulla after dDAVP infusion. Restriction of water intake to increase vasopressin levels also significantly increased TAL ROMK immunolabeling and abundance in immunoblots. In addition, dietary Na+ levels were varied to determine whether ROMK abundance was also affected under other conditions known to alter TAL transport. Rats fed higher levels of sodium, as either NaCl or NaHCO3 (8 mEq/250 g body wt per d), exhibited significantly increased density of the 45-kD band, compared with the respective control animals. Moreover, in rats fed a low-NaCl diet (0.25 mEq/250 g body wt per d), a 50% decrease in band density for the 45-kD band was observed (relative to control rats fed 2.75 mEq/250 g body wt per d of NaCl). These results demonstrate that long-term adaptive changes in ROMK abundance occur in the TAL with stimuli that enhance transport by this segment.

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Knockdown of V-ATPase subunit A (atp6v1a) impairs acid secretion and ion balance in zebrafish (Danio rerio)

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00578.2006 ◽

2007 ◽

Vol 292 (5) ◽

pp. R2068-R2076 ◽

Cited By ~ 78

Author(s):

Jiun-Lin Horng ◽

Li-Yih Lin ◽

Chang-Jen Huang ◽

Fumi Katoh ◽

Toyoji Kaneko ◽

...

Keyword(s):

Acid Secretion ◽

Apical Membrane ◽

Critical Role ◽

Ion Balance ◽

Atpase Subunit ◽

Subunit A ◽

Acid Secreting ◽

And Function

In the skin of zebrafish embryo, the vacuolar H+-ATPase (V-ATPase, H+ pump) distributed mainly in the apical membrane of H+-pump-rich cells, which pump internal acid out of the embryo and function similarly to acid-secreting intercalated cells in mammalian kidney. In addition to acid excretion, the electrogenic H+ efflux via the H+-ATPases in the gill apical membrane of freshwater fish was proposed to act as a driving force for Na+ entry through the apical Na+ channels. However, convincing molecular physiological evidence in vivo for this model is still lacking. In this study, we used morpholino-modified antisense oligonucleotides to knockdown the gene product of H+-ATPase subunit A ( atp6v1a) and examined the phenotype of the mutants. The H+-ATPase knockdown embryos revealed several abnormalities, including suppression of acid-secretion from skin, growth retardation, trunk deformation, and loss of internal Ca2+ and Na+. This finding reveals the critical role of H+-ATPase in embryonic acid -secretion and ion balance, as well.

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Role of PKC isozymes in water transport in toad urinary bladder

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100085812 ◽

1991 ◽

Vol 49 ◽

pp. 302-303

Author(s):

A.J. Mia ◽

L.X. Oakford ◽

T. Yorio

Keyword(s):

Urinary Bladder ◽

Apical Membrane ◽

Membrane Surface ◽

Protein A ◽

Cell Types ◽

Leukemic Cells ◽

Toad Urinary Bladder ◽

Pkc Isozymes ◽

Antibody Labeling

Protein kinase C (PKC) isozymes, when activated, are translocated to particulate membrane fractions for transport to the apical membrane surface in a variety of cell types. Evidence of PKC translocation was demonstrated in human megakaryoblastic leukemic cells, and in cardiac myocytes and fibroblasts, using FTTC immunofluorescent antibody labeling techniques. Recently, we reported immunogold localizations of PKC subtypes I and II in toad urinary bladder epithelia, following 60 min stimulation with Mezerein (MZ), a PKC activator, or antidiuretic hormone (ADH). Localization of isozyme subtypes I and n was carried out in separate grids using specific monoclonal antibodies with subsequent labeling with 20nm protein A-gold probes. Each PKC subtype was found to be distributed singularly and in discrete isolated patches in the cytosol as well as in the apical membrane domains. To determine if the PKC isozymes co-localized within the cell, a double immunogold labeling technique using single grids was utilized.

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The Role of the SLP in Autism Spectrum Disorder Screening and Assessment

Perspectives on Language Learning and Education ◽

10.1044/lle15.2.50 ◽

2008 ◽

Vol 15 (2) ◽

pp. 50-59 ◽

Cited By ~ 1

Author(s):

Amy Philofsky

Keyword(s):

Language Development ◽

Critical Role ◽

Children With Autism ◽

Autism Spectrum ◽

Children With Asd ◽

Prevalence Estimates ◽

Notable Increase ◽

Screening Assessment ◽

Critical Components

AbstractRecent prevalence estimates for autism have been alarming as a function of the notable increase. Speech-language pathologists play a critical role in screening, assessment and intervention for children with autism. This article reviews signs that may be indicative of autism at different stages of language development, and discusses the importance of several psychometric properties—sensitivity and specificity—in utilizing screening measures for children with autism. Critical components of assessment for children with autism are reviewed. This article concludes with examples of intervention targets for children with ASD at various levels of language development.

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